Antigenicity of adult Opisthorchis viverrini, metacercariae and eggs was investigated by radio-immunoprecipitation and polyacrylamide gel electrophoresis using sera from patients with opisthorchiasis and from hamsters experimentally infected with 0. viverrini metacercariae. 125I-labelled aqueous somatic extract and in vitro metabolic products of adult worms, and the extracts of metacercariae and eggs were immunoprecipitated, electrophoresed and autoradiographed and major antigens were characterized. Although components with Mr of > 116, 89, 78 and 20 kD appeared to be specifically associated with the somatic extract of adult fluke, the 89 kD protein was the most prominent component found in the in vitro culture fluid of adult worms and the metacercarial extract. Hamsters, experimentally infected with 0. viverrini, also showed the presence of antibody reactive with the 89 kD component within 15 days of infection. The potential of this antigen in immunodiagnosis is discussed.

The first rigorous proof applicable to the migration pathway of an infective juvenile macroparasite inside its host is presented. Third-stage larvae of a homogonic strain of Strongyloides ratti applied in exact doses of less than 20 to the skin of the flank of young rats were recovered 16–40 h later in the naso-frontal part of the head. The peak proportion of the dose recovered between 20 and 25 h in this site had a mean value of 0·316 ± 0·021 in 48 animals. In 40 other rats infected simultaneously the mean proportion of the dose that reached the small intestine was at least 0·837+0·013. Proof resides in verification of the inequality > 1. With appropriate statistical tests the excess of the sum of the means of these two proportions over unity is shown to have a probability of occurring by chance of 1 in 3·5 × 106. Thus it is effectively certain that the naso-frontal portion of the head is part of at least one pathway taken by this parasite on its way from the skin to the intestine of its host. By suitable protection of the infection site it was confirmed that migration to the head was achieved by an internal route and not as a result of grooming. Larvae were recovered from the cranium in the same rats over the period 15–40 h, but the peak proportion of the dose occurred at 20 h, and < in this location. Whether the cranium is also part of the pathway is therefore still undecided. The significance of this novel analysis in the general context of in-host migration of infective stages is discussed and it is concluded, following its application to data sets from other authors, that the only cases in which proof can be demonstrated are the anterior skull of the rat for S. ratti (present data) and the lung of the same host for Nippostrongylus brasiliensis (Twohy, 1956).

Parasitic helminths excrete or secrete (ES) a variety of molecules into their mammalian hosts. The effects of these ES products on the host's immune responses are reviewed. Investigations into the source of antigenic or immunoregulatory ES products have identified the cuticular and tegumental surfaces of some nematodes and trematodes respectively as being important sources of ES products; other ES molecules are released through specialized excretory or secretory organs. It is proposed that the active shedding of surface antigens may serve as an important source of parasite antigens available to the immune system in a form in which they can be taken up and processed by antigen-presenting dendritic cells, macro-phages and certain B cells for presentation to T helper cells. The ES products of nematodes, trematodes and cestodes contribute to immune evasion strategies of the parasites through mechanisms including shedding of surface-bound ligands and cells, alteration of lymphocyte, macrophage and granulocyte functions and modulation of complement and other host inflammatory responses. Immunopathology may be induced by ES products as in the development of granulomas around entrapped schistosome eggs. In some host – parasite systems ES antigens may induce host-protective immune responses and this source of protective antigens has been utilized in the successful vaccination against helminth infections, particularly against infection with trichurid nematodes and the metacestode stage of cestode parasites. The use of ES antigens in immunodiagnosis of helminth infection is also briefly discussed.

Blatticola monandros Zervos lives in the hind gut of the endemic New Zealand cockroach Parellipsidion pachycercum Johns. A field survey showed that infection prevalence was high (54 %) in small nymphs and increased further with cockroach size to a maximum (92 %) in penultimate nymphs. Variance to mean ratios and the Chi-square test for goodness of fit of a Poisson distribution provide strong evidence that the distribution of the nematode was not clumped (over-dispersed) or Poisson (random) but under-dispersed in most host size classes. The modal infrapopulation type consisted of 1 adult male and 1 adult female. Other infrapopulations were transitional to this type. Monogamous infrapopulations increased in prevalence with increased host size. Juvenile males were uncommon and probably develop faster into adults than juvenile females. Infrapopulations with 2 juvenile males were very rare and no cockroach contained 2 adult males, although some contained 2 adult females. Seasonal variations in prevalence and infrapopulation structure were slight over a 3 year period, except during one unusually dry summer. During the drought, prevalence of monogamous infrapopulations and of transitional infrapopulations were lowest, while prevalence of single-worm and single-sex infrapopulations were greatest. It is evident that competition between females reduces fecundity. When only 1 adult female nematode is present in an adult cockroach, more eggs are produced than the total produced if 2 adult females are present. Eggs were produced cyclically with short periods of high egg production interspersed with several days of very low or no egg production. Most eggs produced on any one day were attached to the outer surface of only 1 of the up-to-6 faecal pellets produced by the host/day. Mechanisms which may regulate infrapopulations and control reproductive competition and cyclical egg production are discussed. It is suggested that B. monandros regulates its own infrapopulation.

The interrelationships between drugs and parasite surfaces are considered under the headings of (a) effects on membrane transport, (b) drug uptake mechanisms and (c) effects on surface morphology and function: praziquantel is discussed under a separate heading. The range of chemotherapeutic compounds that cause permeability changes and concomitant morphological disruption is discussed in terms of mode of drug action. Interpretation of the available data renders it difficult to identify the primary mode of action in the drugs considered. Drug uptake mechanisms are known for relatively few compounds; drug resistance as a function of drug acquisition is discussed. The role of the parasite surface as a specific drug target is argued.

Hookworm infections, as assessed by counting worms expelled following anthelmintic treatment and by egg output, were found to be of low prevalence and intensity in a South Indian fishing community. The initial overall prevalence of infection in the community was 43%, and the average burden was estimated at 2·2 hookworms per person. The age profiles of prevalence and intensity differed between males and females, with the latter harbouring significantly higher levels of infection. Children of both sexes under 10 years of age rarely harboured hookworms. Treatment with pyrantel pamoate was estimated to be 91% effective in clearing hookworm infections. Egg counts made on stools collected during an 11-month period of reinfection indicated that female patients became reinfected soon after treatment, while little hookworm egg excretion was observed in males during the observation period following treatment. Females acquired a significantly higher number of worms during the reinfection period compared with males, although the average burden in females reached only 28% of the initial, pre-treatment level. The hookworm population consisted of predominantly Necator americanus, and less than 10% of Ancylostoma duodenale. The parasites were highly aggregated within the host population with 10% of the community harbouring over 65% of the total hookworms. Low values of the negative binomial aggregation parameter, k, (indicating extreme over-dispersion) were recorded in groups stratified by age and sex. Highly significant positive correlations were observed between the initial (pre-treatment) and reinfection worm burdens of female (but not of male) patients. It is suggested that occupational practices related to walking through areas contaminated with hookworm larvae play an important role in generating the observed patterns of infection within this community.

In the eastern Mediterranean, the copepod Lepeophtheirus thompsoni Baird, 1850, has been reported to infest turbot, brill and flounder. By combining several methods, including enzyme electrophoresis, we show that this species is found only in turbot. By contrast, brill and flounder are infested by a species of Lepeophtheirus that corresponds to no other species reported in the literature. We propose that the species be designated as L. europaensis and we describe the characteristics of the gravid female. This study was extended to the Atlantic populations of flatfishes and includes an investigation of L. pectoralis (Muller, 1776), which infects flounder in the North Sea; we also confirmed the presence of L. thompsoni (Baird, 1850) over the whole geographic range of turbot. Lastly, we discuss the specificity and distribution of these species along the European coasts.

Experimental infection of adult Drymaplaneta variegata Shelford, 1909 (Blattodea) with known numbers of eggs of Protrellus dixoni Zervos, 1987 (Nematoda: Thelastomatidae) showed that each infrapopulation was regulated by a density-dependent and sex-dependent reduction in infection intensity with infrapopulation age. This reduction was not equal in initial speed or intensity between the sexes (reduction in number of males was faster) and led to infrapopulations with never more than a single adult male, 1–8 (usually 1–3) adult females and 0–28 juvenile females. In structure, these laboratory-produced infrapopulations resembled those in field-collected hosts. Parasite-mediated chemical interference competition is suggested as the cause of infrapopulation regulation. Per capita egg production was greater in uncrowded worms which suggests that self-regulation benefits those nematodes that survive competition. Unmated females produced male offspring only (probably by arrhenotokous parthenogenesis). Only females that occurred with a male produced females although some also produced males; such females may avoid insemination or prevent fertilization of some or all eggs. Female offspring probably result from amphimixis.

The uptake of cycloleucine, L-proline, L-alanine and L-threonine by secondary hydatid cysts of Echinococcus granulosus (U.K. horse strain 3–8 mm in diameter, derived from Balb/c mice infected 300–400 days previously) occurs by passive diffusion into the cyst wall (laminated layer plus germinal layer) and by mediated mechanisms into the fluid-filled interior. The maximal concentrations of these compounds are achieved after incubation for 2 h in vitro and approach those in vivo. Kt and Vmax values describing the uptake of these compounds are given. The flux rates for these compounds are extremely slow compared to those obtained with the protoscolex. A rationale for standardizing the experimental method for uptake studies with hydatid cysts is described.

The availability of restriction fragment length polymorphisms (RFLPs) would be useful for studying the extent of diversity among morphologically indistinguishable populations of filarial parasites. Such polymorphisms may be useful in correlating various physiological and clinical differences with parasite heterogeneity. In order to identify such RFLPs, we isolated DNA from microfilaria of 6 filarial species (Acanthocheilonema viteae, Brugia malayi, Brugia pahangi, Dirofilaria immitis, Litomosoides carinii and Setaria digitatum), digested the DNA with several restriction endonucleases, prepared Southern blots and probed with 32P-labelled DNA probes. The patterns of fragments generated using two restriction endonucleases, Mbo I and Tag I, in combination with two probes, rDNA from the free-living soil nematode Cenorhabditis elegans, and pBM103, an anonymous DNA probe from B. malayi, unequivocally distinguish between all 6 of the species. To ensure that the differences we observed between the species represent true interspecies variation rather than fortuitous individual variations we analysed DNA from several individual B. malayi and B. pahangi worms. The individual B. malayi worms demonstrated restriction profiles that were invariant, as did the individual B. pahangi worms, demonstrating that the differences we observed were true interspecies variations.

Cerebral malaria in A/J and CBA/H mice infected with Plasmodium berghei ANKA is accompanied by mononuclear cell infiltration, haemorrhage and cerebral endothelial cell damage. This damage is presumably one of the causes of the breakdown of the blood—brain barrier which was detected by measuring the movement of the dye Evans blue and radioisotope labelled albumin and erythrocytes. The density of brain tissue, measured by a Percoll gradient technique, was significantly reduced in mice exhibiting cerebral symptoms, suggesting the occurrence of cerebral oedema.

Polychromophilus murinus, a malaria parasite of Chiroptera is reported from Myotis daubentoni in England. The vector was suspected to be the ectoparasitic Nycteribiid fly, Nycteribia kolenatii. N. kolenatii collected from wild-caught M. daubentoni were found to have oocysts on the midgut and sporozoites in the salivary glands. Wild-caught N. kolenatii were maintained on two wild-caught M. daubentoni harbouring heavy (patent) infections of P. murinus; both oocysts and sporozoites were found in these flies. The mature oocysts measured 52–71 μm in diameter. Sporozoites were straight or slightly crescentic and had a mean length of 7·4 μm. Electron microscopy of immature and mature oocysts revealed a morphology similar to that of malaria parasites. Sporozoites were also similar in structure to Plasmodium sporozoites and were found in the epithelial cells of the salivary gland and within the lumen; a cytostome was present and transverse sections revealed 21 microtubules arranged evenly around the periphery. Sporozoites were observed within the basement membrane of the salivary gland of N. kolenatii; such sporozoites appeared to be penetrating the gland, a process hitherto not described in malaria parasites. Rickettsia-like bodies were found within the cytoplasm of the epithelial cells of the salivary gland. Exflagellation of microgametocytes was achieved. An ultrastructural study of the gametocytes revealed a structure similar to that described in other Haemoproteidae. A common feature of infected erythrocytes was a projecting erythrocyte membrane. Attempts to find schizogony in impression smears and sections of tissues of two infected M. daubentoni were not successful.

A Theileria parva lawrencei isolate in the form of a sporozoite stabilate, derived by feeding clean Rhipicephalus appendiculatus nymphal ticks on an African buffalo (Syncerus caffer) captured in the Laikipia District, Kenya, was inoculated into groups of cattle at dilutions between 100 and 10-3. Groups of 3 cattle infected with 1 ml inocula at 100, 10-1 and 10-2 dilutions were treated with 2·5 mg/kg body weight of buparvaquone on day 0 and similar groups were left untreated to act as controls. An additional group, given 100 dilution of the stabilate, was treated with buparvaquone on day 8 post-inoculation. It was found that all control cattle inoculated with the stabilate at dilutions between 100 and 10-2 became infected, but only 2 out of 3 cattle developed patent infections at 10-3 dilution. All 3 control cattle receiving 100 dilution died of theileriosis, 2 at 10-1 and 10-2 dilutions, and 1 at 10-3 dilution died. Buparvaquone treatment on day 0 at 100 dilution resulted in the survival of 2 of 3 cattle and all the cattle at 10-1 and 10-2 dilutions. All the surviving cattle eventually developed a significant serological response against T. parva in the indirect fluorescent antibody test, except 1 in the 10-3 dilution group, and were immune to homologous challenge when tested 3 months later with a lethal inoculum of stabilate, except 2 cattle in the 10-3 dilution group. As a result of a theileriosis problem at about day 60 after inoculation in 2 cattle given 10-2 dilution of stabilate and buparvaquone treatment on day 0, an additional 5 cattle were given 10-2 dilution of stabilate and developed a good immunity after buparvaquone treatment. None was shown to develop the carrier state. Treatment with buparvaquone on day 8 after infection with 100 dilution of stabilate was not successful since 2 died. The stabilate used was shown to produce reproducible infection in cattle at different dilutions.

The metabolites of 5-hydroxytryptamine (5-HT, serotonin) namely, L-tryptophan, 5-hydroxytryptophan, 5-hydroxyindole acetic acid and 5-hydroxytryptophol were measured in perfused tissue and whole worms from adult female Ascaris suum using reversed-phase liquid chromatography with electrochemical detection. The intracellular levels of each metabolite were quantitated in response to several physiological effectors but only Ltryptophan (TRP) caused dose-dependent changes in these metabolites. Serotonin itself could also be absorbed by perfused A. suum muscle and intestinal tissue. When live A. suum were tied at the anterior and posterior regions to restrict TRP absorption by the intestine, TRP was absorbed through the cuticle and converted into 5-HT by the muscle tissue. In untied live parasites TRP absorption was observed in both muscle and intestinal tissue. Collectively, the data indicated that 5-HT may be either absorbed directly or synthesized de novo from absorbed TRP in the isolated tissue of A. suum. The 5-HT, in the live adult female A. suum, can be synthesized de novo from TRP, or 5-HT can be absorbed from the environment both through the cuticle and by the intestine of living parasites. Data also indicated that there was preferential sequestering of 5-HT and the metabolites of 5-HT in the anterior tissues of the worms.

The problems caused by tick and tick-borne diseases for livestock particularly cattle on the African continent are described and discussed. The control of ticks and tick-borne diseases must receive high priority in Africa with regard to both research and control application because of their widespread distribution in areas of high livestock potential and productivity. The conventional methods of tick and tick-borne disease control are discussed and are found to be inadequate in the conditions prevailing in Africa. Methods of integrated control are suggested and discussed in light of recent development in control methods and those still under development. Any one of these methods may not be adequate to control the problem on its own but when several of the methods are combined an economic and robust integrated control is likely to result. Encouragement is given to attempt this approach in Africa to solve what must be the largest animal health problem of livestock remaining in the world.

Several species of malarial protozoans commonly parasitize the same host population and often the same individual host. This paper reviews the evidence for interactions among such host-sharing parasites. Field studies measuring the cross-sectional prevalence of malarial species often record fewer mixed infections than expected by chance, suggesting that one parasite has excluded another or suppressed its parasitaemia to undetectable levels. Prevalences may vary reciprocally between seasons, with one species increasing in prevalence while another decreases, despite parallel increases in the transmission rates of both, again suggesting suppression of one species by another. However, longitudinal studies of individual hosts indicate that malarial parasites may also favourably affect the host environment for each other, perhaps due to their depressive effect on the immune system: this is shown by the recrudescence of a latent malarial species immediately before or after the parasitic wave of another species. The suppression hypothesis is supported by data derived from the simultaneous inoculation of two Plasmodium species into laboratory animals; many studies have shown that one or both species are suppressed. This may be mediated by competition for host cells or nutrients, or by heterologous immunity. However, the suppressed species rebounds after the other species has abated, and may show a prolonged infection. Experimental evidence that one species can facilitate the recrudescence of another is minimal, but this may reflect the paucity of investigations of this phenomenon. Laboratory studies show only minor cross-resistance between host-sharing species, which is consistent with the hypothesis that their co-occurrence has led to antigenic divergence or that species showing strong heterologous resistance cannot co-exist in the same host population. Such complementarity occurs not only with the host immune response but also with many other life-history characteristics of host-sharing parasites, such as host cell preference. I conclude that malarial species have been important in each other's evolution, particularly in the tropics where multi-species complexes are common.

Analysis of egg and worm counts of Ascaris recorded at various intervals following a mass anthelmintic treatment programme in a South Indian fishing community is presented. Three indices of infection in the community are compared, namely the prevalence and intensity of egg output (at 2, 6 and 11 months following treatment) and the number of worms expelled following an 11 month period of reinfection. Detailed examination of these measurements revealed significant associations with patient sex and age. The age-prevalence profile of Ascaris infection changed little over time (except immediately following treatment) with the peak prevalence found in the 5–9 year age group. Although 85% of both males and females harboured Ascaris initially, the prevalence following 11 months reinfection was decreased, due to a significantly lower proportion of males being reinfected. By the 11th month of reinfection, the age-intensity profiles of egg output were similar to those observed at initial treatment in the older age groups (10 years and above) and in male children (< 10 years). However, a dramatic increase in the egg output of female children, greatly exceeding the initial mean, was observed within a 6 month period of reinfection. The intensity of egg output did not accurately reflect the abundance of Ascaris recovered via drug-induced expulsion following an 11 month period of reinfection. Although the egg output attained preintervention levels, the average worm intensity reached only half the initial value. The trends in the sex- and age-intensity profiles were consistent at the two sampling dates and showed similar patterns to the egg output curves. The relevance of the results to helminth control and the monitoring of reinfection is discussed.